1. Field of the Invention
This invention relates generally to apparatus for slitting coil stock and more particularly to an apparatus for the precision slitting of light gage stock, such as black plate, into multiple continuous lengths of high quality wire.
2. Description of the Prior Art
One of the more common mill conversion processes a metallic coil undergoes is slitting. Generally speaking, a wide coil is slit into a number of narrow multiples on a slitting line. Such a line includes an uncoiler for positioning and feeding the coil into a slitter and a re-coiler for rewinding the slit strands into tightly wound narrow coils. Two factors, economics and specific technical requirements, are of paramount importance in the design and operation of all slitting lines.
The slitting operation itself is accomplished by two sets of circular cutters mounted on parallel arbors and with the respective cutters set in a staggered sequence. The cutters are also aligned and overlapped in such a manner so as to cause a shearing action to take place when metal is forced between them during slitting. There are many factors affecting the economics of a successful and profitable slitting operation. Some of these factors include material, hardness of material, maximum and minimum thickness of material, coil diameter and weight and coil handling facilities. The techical requirements involved in designing a line to perform economically must therefore consider all these factors. For example considering the present state of the slitting art, it is not commercially feasible nor economically practical to slit coil stock into multiples with a cross-sectional area of approximately 7.0 .times. 10.sup.-.sup.4 square inches. It is also recognized that slitting stock with an aspect ratio of less than about 5 cannot be practiced on a commercial basis.
The conventional slitting operation of the prior art, employs a pair of parallel top and bottom arbors with a specifically arranged set-up of knives, spacers and shims. These components are carefully designed and machined to close tolerances from alloy steels. The specific slitting operation, viz. material and slit width, control the component design. What is known in the art as "setting up slitting arbors" consists of first placing a knife on the top arbor and then placing a spacer equal in thickness to this knife on the bottom arbor. A knife is then placed adjacent to the spacer on the bottom arbor and a spacer equal to the width of the strip to be cut is then placed on the top arbor, the next step is to place a spacer equal to the width of the strip to be cut on the bottom arbor. Shims are carefully placed along the length of the arbor depending upon such factors as clearance and material to be slit. This procedure of placing spacers, knives and shims is continued alternately on the top and bottom arbors until the last pair of knives and spacers have been added. After the arbors are set up, the bottom arbor is placed into a housing and the top arbor is then lowered and placed into the housing so that the knives overlap and satisfactory knife clearance is established. It is quite apparent that such a set up is both laborious and expensive.
The width of the slit material is controlled by the width of the spacers employed. Steel coil stock is currently slit into widths exceeding about one-half inch and with aspect ratios greater than 5 on a commercial basis. The aspect ratio is defined as: ##EQU1##
For example, to slit a cold rolled 20 gauge, 0.0368 inch, 24 inches wide coil into 6, 4 inch multiples the aspect ratio would be approximately 110 and would decrease to 55 for 2 inch multiples and so forth to approximately 14 for 1/2 inch multiples. To slit black plate coil stock, wherein black plate hereinafter is defined as, a product of the cold-reduction method in gages No. 29 and lighter (thickness 0.0141 inch and under), into widths narrower than one-half inch (0.500 inch) would require smaller aspect ratios because of the smaller width of the slit multiple.
For example, to slit a 0.0141 inch thick, 24 inch wide black plate coil into 340, 0.0705 inch wide multiples would require an aspect ratio of 2. To accomplish such a slitting operation several hundred knives and spacers would have to be placed alternately on arbors as hereinbefore described. A set-up technique would require the ability to measure the thicknesses of the spacers and knives to extreme levels of accuracy, and elaborate precautions in matching and stacking them on the arbors so that tolerance accumulation would occur in a like manner on both arbors. Furthermore, due to the very small cross section of the knives and spacers, warpage, breakage and curling resulting from machining all become problems. Using knives with such a small cross sectional area also poses problems in cutting because the actual force which can be applied during slitting is greatly restricted.
Aside from the actual slitting operation the slit product frequently must also meet very stringent quality requirements. Assuming that slitting arbors can be so assemblied from knives, spacers and shims, for certain critical applications the resultant product must have minimum burr formation and good mechanical properties particularly high fatigue resistance. Furthermore, uniformity must be present between adjacent and neighboring multiples. To achieve acceptable mechanical properties the slit product must be burr free and have a generally rectangular or square cross-sectional configuration. A slitter consisting of knives, shims and spacers could not produce a slit product with the aforementioned characteristics and an aspect ratio of less than 5 because arbors with stacked mates can not be matched thereby resulting in excessive variations in tolerances.
The present invention enables light gage coil stock of less than approximately 29 gage such as conventional black plate to be rapidly and economically slit into multiples with an aspect ratio of less than 5.